f(x)=lim(n->∞) (1+x)/(1+x^(2n))
case 1: x<-1
f(x)=lim(n->∞) (1+x)/(1+x^(2n)) = 0
case 2: x=-1
f(-1) = (1-1)/(1+1) =0
case 3: -1<x<1
f(x)=lim(n->∞) (1+x)/(1+x^(2n)) = 1+x
case 4: x=1
f(1)= (1+1)/(1+1) = 1
case 5: x>1
f(x)=lim(n->∞) (1+x)/(1+x^(2n)) = 0
ie
f(-1-) =f(-1) =1
f(-1+)= lim(x->-1+) (1+x) =2
x=-1 跳跃间断点
f(1-)=lim(x->1-) ( 1+x) =2
f(1) =1
f(1+) =lim(x->1+) 0 =0
x=1 跳跃间断点